This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Prior studies in this project have characterized age-related changes in cognitive performance in the rhesus monkey. The data obtained has been used as the basis for studies of the changes in the brain which underlie normal cognitive decline, as well as changes in motor function. Our studies have permitted us to characterize the influence of hormonal and sex-related variables on cognitive performance and to relate changes in monoamine receptors in relation to cognition. The basic cognitive domains we have examined include recognition memory, spatial working memory, and implicit memory. We have conducted behavioral tests and structural MRIs on 9 rhesus monkeys. All of the monkeys were grossly normal in terms of gross brain morphology as detected in the MRIs. Behavioral tests, designed to trace cognitive decline in these animals, have been completed in 4 of the animals which have been shipped to Boston University School of Medicine where their brains will be studied at the neuorophysiological, neurochemical, and neuroanatomical levels. This work will continue to clarify which neural changes lead to age-related changes in cognitive ability and which neural characteristics are associated with relative resistance to cognitive decline.